Popular Science Monthly 



7(>JJ 



Holding a Board with the Weight 

 of a Newspaper 



AVERY singular experiment can be 

 carried out with a board about 3 ft. 

 long and a piece of paper. A newspaper 

 will do. The board is placed on a table 

 with one-third of its length projecting 

 over the edge. Cover the part of the 

 board that is on the table with the news- 

 paper, then ask one of your friends what 

 will happen if you give the projecting end 

 of the board a sharp blow downward with 

 the fist. Most people will say that the 

 board will spring off the table. But this 

 is just what it will not do. Providing the 

 blow be very sudden, the board will be 

 immovable, no matter how hard the 

 knock may be. The board should not be 

 too wide so that a goodly portion of the 

 paper will lay on the table top. 



The explanation of this curious fact is 

 to be found in the pressure of the air. It 

 should be borne in mind that in the 

 ordinary way the atmosphere is pressing 



The board and the paper as they are 

 placed on the table top for the experiment 



on every side of objects on this earth with 

 an even weight. If the board on the 

 table is given a sharp blow, there is no 

 time for the air to rush beneath the paper 

 to the underside of the board which is 

 close to the table. As a consequence, 

 there is a tremendous pressure on the 

 upper part of the board, but none on the 

 under part. This weight of air is so great 

 that the board will break, if the blow is 

 hard enough, before it will jump off the 

 table. On the other hand a slow pres- 

 sure, even wnth the little finger, will easily 

 move the board. This is owing to the 

 fact that the air has time, in these circum- 

 stances, to pass underneath the board 

 and newspaper — S. Leonard Bastin. 



A Homemade Wrench for Turning 

 Small Inaccessible Nuts 



THE little wrench shown in the il- 

 lustration was made of an old foot 

 pump handle. The parts being round it 

 was only necessary to drill holes through 



Wrench made from a foot pump rod that 

 will work like an ordinary monkey wrench 



the movable jaw and the adjusting cli| 

 then cut threads of the latter as well as oh 

 the handle for making the wrench com- 

 plete. Two nuts hold the adjusting piece 

 on the outer jaw end. This wrench is an 

 excellent one to use when making repairs 

 on an automobile because it turns small 

 nuts placed in places that are otherwise 

 inaccessible. — Kenneth Whitney. 



Homemade Hectograph for Making 

 Copies of Letters 



A COPYING pad is indispensable to 

 those who wish to make a limited 

 number of copies of writings or drawings. 

 One which is practical as well as in- 

 expensive may be constructed in the 

 following man- 

 ner •, Procure 1 

 oz. of the best 

 gelatine; cover it 

 well with cold 

 water, and allow 

 it to stand over- 

 night, care being 

 taken to see that 

 all of it has 

 swollen. Heat 6 



oz. of chemically pure glycerine over a 

 salt water bath to a temperature not ex- 

 ceeding 200 deg. F. The water that has 

 not been absorbed by the gelatine should 

 be poured off, and the gelatine added to 

 the hot glycerine. The mixture obtained 

 is heated for about an hour, and gently 

 stirred occasionally, avoiding as much as 

 possible any tendency of the fluid to froth 

 or bubble. At this point add about a 

 teaspoonful of oil of cloves as a preserva- 



The gelatine mixture 

 placed in a shallow pan 



